2-Alkylpyrimidines, particularly 2-tert-butylpyrimidine, are advantageously employed as intermediates for the preparation of insecticidal O- -alkyl-O-pyrimidin-(5)-yl]-(thiono)(thiol)-phosphoric (phosphonic) acid esters or ester amides as described in U.S. Pat. No. 4,127,652.
The preparation of 2-alkylpyrimidines is taught in U.S. Pat. No. 3,050,523. That process requires the reaction of an alkylene 1,3-diamine with an organic carboxylic acid, ester or amide over a supported noble metal catalyst having dehydration and dehydrogenation activity. The desired compounds may be isolated by azeotropic distillation or by treatment with carbon dioxide followed by distillation. The work-up procedures are time consuming and the yields are not as good as could be desired.
More recently, the individual steps (a-c) of the conversion of 1,3-diaminopropane and an alkanecarboxylic acid to a 2-alkylpyrimidine have been investigated; see, for example, U.S. Pat. Nos. 4,376,201 and 4,493,929 and European Patent Application Publication Nos. 117,882, 192,297 and 192,299. ##STR1##
U.S. Pat. No. 4,376,201 describes the vapor phase reaction wherein a 3-aminopropyl carboxylic acid amide is cyclized and dehydrogenated over a supported platinum or palladium catalyst (steps b+c).
U.S. Pat. No. 4,493,929 describes the separation of steps b+c and the improved vapor phase reaction wherein 2-alkylpyrimidines are obtained in high yield and purity by the dehydrogenation of a 2-alkyltetrahydropyrimidine under conditions which do not generate water and in which no water is added (step c).
European Patent Application Publication No. 117,882 describes an overall process for the preparation of 2-tert-butylpyrimidine which comprises the following individual steps: a) the preparation of 3-aminopropyl pivalamide by reaction of pivalic acid and an excess of 1,3-diaminopropane: b) removal of unreacted 1,3-diaminopropane by distillation and dehydration of the 3-aminopropyl pivalamide to 2-tert-butyl-1,4,5,6-tetrahydropyrimidine in the liquid phase, preferably in the presence of a solvent capable of azeotroping water: and c) the dehydrogenation of 2-tert -butyltetrahydropyrimidine to 2-tert- -butylpyrimidine, under conditions in which water is neither generated nor added, over a supported noble metal catalyst.
European Patent Application Publication No. 192,297 describes the vapor phase dehydrogenation of 2-propyl- or 2-butyl-1,4,5,6-tetrahydropyrimidine over a palladium containing catalyst in which the catalyst lifetime is prolonged by operating the presence of carbon monoxide and hydrogen (step c).
European Patent Application Publication No. 192,299 describes the multistep preparation of 2-methyl- and 2-ethylpyrimidine by: the reaction of an acetic or propionic acid derivative with 1,3-diaminopropane in the liquid phase to form a 1-amino-3-amidopropane (step a): optional cyclization to the 2-methyl- and 2-ethyltetrahydropyrimidine (step b): and gas phase dehydrogenation and optional cyclization to 2-methyl- and 2-ethylpyrimidine with a palladium-containing catalyst in the presence of carbon monoxide and hydrogen (step c or steps b+c).
Thus, although the direct conversion of 1,3-diaminopropane and an alkanecarboxylic acid to a 2-alkylpyrimidine was originally conceived in U.S. Pat. No. 3,050,523, the cumbersome work-up procedures and poor yields of that original disclosure prompted subsequent researchers to recommend improved stepwise approaches to the desired conversion.